In recent years significant progress has been made in our understanding of transport and metabolism of water-soluble vitamins by intestinal epithelia. The investigators will continue to explore this expanding field. The related topic of renal handling of water-soluble vitamins has attracted little research attention in spite of an important role the kidney plays in controlling circulating vitamin levels by reabsorption, secretion, and metabolism of these substances. We will extend our preliminary observations which indicate participation of the mammalian kidney in handling three vitamins of interest. Research effort will be directed at understanding ascorbate metabolism in the stomach and intestinal lumen, and the mechanism by which ascorbic acid exits enterocytes toward the blood. Renal handling of ascorbic acid will be examined in kidney by clearance techniques; transport properties that are indicated will be evaluated with vesicles made from cell membranes. Ongoing studies of nicotinic acid uptake in kidneys of rat and chicken will be extended by analyzing for metabolism of this vitamin during transport. The specific location of the transport step will be analyzed with vesicles. Our prior study on nicotinamide absorption in the chicken intestine will be followed up with studies in vesicles preparations where transport can be examined in the absence of vitamin metabolism. The overall handling of nicotinic acid and nicotinamide by mammalian and chicken kidney will be examined with appropriate clearance techniques. Little is known about how the intestine and kidney handle pantothenic acid. In preliminary studies we have identified tissue preparations and analytical techniques that appear to be appropriate for in-depth studies of this vitamin. Uptake and metabolism in isolated perfused segments of small intestine will be assessed. The characteristic of uptake across the brush border of intestine will be determined by measuring unidirectional influxes in vitro. Overall renal handling of pantothenic acid will be determined by clearance techniques. Renal metabolism of pantothenic acid will be determined by the kidney slice technique in vitro. Properties of transport across the cell membrane in the absence of metabolism will be identified with vesicles when appropriate.